Synchronizing system for airplane machine guns



Dec. 17, 1940. J. P; GATY ETAL SYNCHRONIZING SYSTEM FOR AIRPLANE MACHINE GUNS Filed Aug. 19, 1958 6 Sheets-Sheet 1 .INV ENTO RS John P. Qafz BY Irvi Doyle mph m, M T

ATTORNEYS Dec. 17, 1940. P Y ET AL 2,225,599

SYNGHY CONIZING SYSTEM FOR AIRPLANE MACHINE GUNS- Filed Aug. 19, 1958 s Sheets-Sheet s at o n D le BY Irving W p? ATTO Dec. 17, 1940- J P, GATY ETAL 2,225,599

SYNCHRONIZING SYSTEM FOR AIRPLANE MACHINE GUNS Filed Aug. 19, 1938 6 Sheets-Sheet 4 Dec. 17, 1940. J. P. GATY ETAL 2,225,599

SYNCHRONIZING SYSTEM FOR AIRPLANE MACHINE GUNS Filed Aug. 19, 1938 6 Shuts-Sheet 6 INVENTORS John P. Goth) BY Iruz'n' W ,Doyle Twa Patented Dec. 17,1940

- ;I; UNlTED aSTATE s- PATENT OFFICE,

simcnnomzmo SYSTEM FOR momma GUNS John'l. Gaty, Wichita, Kana, and Irving 'W.

Doyle, Amityville, N. Y., assignor to Fairchild Aerial CameraCorporation, a corporation of New York Application August 19, 1938, Serial No. 225,090

. 13 Claims. This invention relates-to apparatus for synchronizing the firing of a m'achinegun with the f rotation of an airplane propeller.

' One of the objects of this invention is to provide a machine gun synchronizer characterized by simplicity. reliability and durability over an extended period of use. Another object is to provide a machine gun'synchronizer which is capable of controlling the firing of the gun so that the'bullet will pass through the plane of rotation of the propeller without striking the propeller blades. Another object is to provide a machine gun synchronizerwhich operates efliciently at the synchronizing system assembled with a ma- I chine gun mounted in firing relationship to an airplane motor and propeller;

Figure 2- is a section taken through the trigger motor-which is attached to the machine gun,

V a portion of the gun also being shown in-sectiom Figure 3 is a horizontal section taken along the line 3-3 of Figure 2;" s

Figure 4 is a sectional elevation of the timing device which forms a part of the synchronizing system;

Figure 5 is a fragmentary horizontal section taken along the line 55 of Figure 4, a portion being broken away;

Figure 6 is a horizontal section taken along the a line 6-6 of Fi e 4;

Figure 7 is a fragmentary vertical section of a modified form of trigger motor;

Figure 8 is a diagrammaticelectric circuit of the synchronizing system;

7 Figure 9 is a modification of a portion of the circuit shown in Figure 8,

Figure 10 is afragmentary vertical section of another modification of the trigger motor; and

- Figure his a fragmentary perspective view of a'portion of the timing mechanism shown in Figure 4. v

Similar reference characters refer to similar *partsthroughoutthe several views of :the drawings.

- While synchronizingv systems for synchronizin airplane machine gun fire with the propeller have long been in use, numerous difilculties have been 3 inherent therein which seriously limit the cfllciency of the gun, and often result in expensive andsometimes fatal damage to the airplane.

This is particularly true of mechanical systems of synchronization, which in spite of almost continuous development have always required careful' attention, not only by the pilots who operate the guns, but also by those whose duty it is to attend to the care and adjustment aspects. Skilled ordnance men are almost prerequisite in caring for the synchronizers, and for obvious reasons such skilled attention is not always available.

The increasing use of three-bladed propellers has caused fundamental and substantial dimculties in applying common types of synchronizing systems, and these difliculties have seriously restricted the speed range of they engine atwhich the machine gun can safely beflr'ed without the bullets striking the propellers. ,This will be readily understood when thehigh speed of modern airplane engines is taken into consideration, plus the fact that these engines are driving threebladed propellers. 7

As is well known, it is desirable that the bullet from the gun pass through the plane ofrotation a of the propeller at a point substantially bisecting the angle between adjacent blades. 1 In order to accomplish this condition at normal operating speeds the system is adjusted to actuate the firing mechanism immediately following the passing of the line of fireby any propeller blade at'substantially zero R. P. M. This point is called and will hereinafterbe referred to as the zero shot." It

is obviousthat any substantial deviationfrom the median line between two adjacent blades, particularly when the gun is so positioned that the bullets pass through the plane of rotation of the propeller at a point nearer the'propelle'r hub than the propeller tips, would cause damage to the propeller by the bullets striking it. Substantial deviation from the zero shot position is inevitable in any of the synchronizing systemsnow in use, because of certain time lag constants inherent in any synchronizing system. Forexampie, the period of time between the instant the firing cycle is initiatedand theinstant the bullet passes through the plane of rotation of the propeller is of the orderof .008 of a' 'second. This lapse or'lag is a constant, it isoccasione'd by inertia of parts, necessary clearancetherebetween, friction losses,time of powder burning and time of bullet flight from the ,gunblock breach to theplane of rotation of the propeller.

; It readily apparent thenthat if the zero shot is set to obtainpassage of the bullet through the plane of rotation of the propeller at median line between'blades ata'ny givenengine or. propeller speed, the position of bullet passage relative to adjacent blades'will vary as the engine speed varies, i. .e. at engine speedslowerthan that at which the. zeroshot is set, the bullets willipass through the plane of rotation of the propeller closer to the preceding blade, whereas at engine speeds higher than the set speed, the bullets will pass through the plane of rotation of the pro- 8 peller closer to the following propeller blade. Thus it appears that it is desirable to change the position of the zero shot as the engine speed changes to prevent damage to the propeller.

Heretofore efiorts havebeen directed toward 10 the reduction of the time lag between trigger release and passage of the bullet through the plane of rotation of the propeller. However, be-

cause of the use of three-bladed propellers and high speed motors, this time lag cannot be reduced sufliciently to result in safe and eflicient machine gun operation at high engine speeds. Furthermore, where dependence has been placed on reduction of time lag, indifferent results have been obtained because of diiliculty of adjustment, excessive motor speeds, breakage of rapidly moving parts, etc.

Electrical synchronizing systems also present, in addition to those above, other dimculties resulting from structural complexity, excessive power requirements, undue weight, delay in operation, etc. Systems of this nature which utilize an intermittently energized solenoid are unsatisfactory because of the inherent current build-up lag and the consequent force build-up lag which 0 results in a change of phase of the firing position with relation to the propeller blades as the force requirements necessary to fire the gun change with changing temperatures. It is accordingly another object of this invention to provide a machine gun synchronizing system which obviates these various difiiculties in a practical and efficient manner.

With reference to Figure 1 of the drawings, a machine gun generally indicated at is operatively mounted on an airplane (not shown) in relation to a motor 2| which drives a threebladed propeller having blades 22, 23 and 24. Gun 29 is so aimed as to fire through the plane of rotation of the propeller at a point designated X, this point being the zero shot position and bisecting the angle between adjacent blades, such as blades 22 and 23. A trigger motor, generally indicated at 25 is suitably secured to the side of machine gun 28 and is electrically connected by wires 26 and 21 and a ground wire 9 to an automatic timer generally indicated at 28 operatively mounted on and having a driving connection with motor 2|. Timer 28 is in turn electrically connected by wires 29 and 36 to a junction box 3|, from which wires 32 and 33 lead to a hand switch 34 mounted on the control stick 35 of the airplane. A battery 36 is connected to wire 33. As will be more fully described hereinafter, when the pilot pulls trigger or switch handle 34a, a circuit is completed to trigger motor 25, this circuit being intermittently made and broken by timer 28- to fire the gun synchronously with respect to the propeller rotation.

Referring now to Figure 2, a trigger motor 25 includes a casing 31 having a mounting plate 38 on which are formed suitable gibs 39 and 40 or the like adapted to fit into ways 4| formed in a side 42 of gun 20. Gib 49 is secured to the end of a threaded stud 43, and when a nut 44, threaded on stud 43, is taken up against the rear of mounting plate 38, gib 48 is drawn against gun side 42 to securely hold the trigger motor in place on the gun.

Casing 31 includes an annular portion 31a into which a metal ring or shell 45, formed of magbeing insulated from netic material, is set, this shell being held in place by screws 46 or ,thelike. The bottom of shell 45 is preferably cut away at 46 to form an annular shoulder 41 against which a cap 48, preferably of soft iron, is set. A central bore in cap 5 48 receives a core 49, which extends upwardly, as viewed in Figure 2, through shell 45 and forms therewith an annular space 59 in which a field winding 5| is disposed. The other end of shell 45 also has an annular shoulder 52 against which 10 an iron ring 53 is set and held in any suitable manner.

The upper end of core 49 is reduced as at 54 to provide an annular space or air gap 55, which receives the peripheral portion 56 of a floating l8 cage 51. Cage portion 56 is suitably recessed to receive an armature coil or winding 58, the convolutions of which are preferably rectangular in cross section, and the upper end of which is secured to a resilient lead or conductor 59. Conductor 59 is held by a screw 60 extending through a bracket 6|, the shank 68a of screw 66 being insulated from bracket 6| by an insulating piece 62. A nut 63 threaded on the end of the screw secures a contact 64 thereon, the contact also bracket 6| by the top of insulator 62.

As viewed in Figure 3, conductor 59 is bolted to a plate 65, which is riveted or otherwise secured to cage portion 56, but is also insulated therefrom, plate 65 being connected to the upper end of armature coil 58 (Figure 2). Preferably a second conductor 66 (Figure 3) substantially similar to conductor 59 is secured to the other end of armature coil 58 for connection to a ground 35 wire.

Referring back to Figure 2, the upper part of bracket 6| has secured thereto in any suitable manner an annular cage or housing 61, which houses the upper end of a'coil spring 68, whose 40 lower end bears against the top 69 of cage 51, top 69 preferably being substantially in the form of an inverted cone. Extending upwardly from cage top 69 is a shell-like projection 19 whoseupper end 1| is provided with a bearing surface 45 which slidably fits within housing 61. A guide generally indicated at 12 is formed within cage projection 19 and includes a semi-tubular portion 13 terminating in a partially spherical support 14, which cooperates with a semi-spherical depression 15 in cage top 69 to rotatably retain the spherical end 16 of a plunger 11 whose shank 18 extends through semi-tubular portion 13 into way 4| formed in gun 20. The end of plunger 18 is aligned with the sear 19 of the machine gun to effect operation thereof as will be pointed out below. As noted, this spherical end 16 of plunger 11 is rotatably mounted, i. e., it may rock about the axis of its end 16. Preferably a spring secured to cage top 69 urges plunger shank 18 against the semi-tubular portion 13 of support 12, but permits counterclockwise rocking of the plunger to a limited extent to permit recharging of the gun without damage.

The under portion of cage top 69 has a boss 8| which rests against the top of a stop 82 secured to the top of core 49 by a screw 83. The outer end of plunger 18 is spaced from sear 19 so as to provide a hammer blow against the sear. Thus when unenergized the cage 69 and 70 plunger 18 are held in the position shown in Figure 2 by spring 66. The outward thrust of the plunger is limited by the travel of cage 51. Face 51a of cage 51 strikes face Ila of bracket 6| and is positively stopped thereby. 75

I 10 58 is energized by current flowing from terminal 85, cage and accordingly plunger 11 is projected upwardly to actuate sear 18. when ar- I mature 58 is deenergized, spring68 returns the several parts to their rest position against stop 15, 82. To prevent rotation of .cage 51 and its con .nected parts during operation thereof, suitable guides 81 and 88 (Figure 3) are provided. These. guides are secured to bracket 8| and include projections 88 and 88 respectively, which extend 20 into slots 8| and 82 (seealso'Figure 2). formed in cage' portion 56, thus preventing rotation of the "cage in either direction about the axis ofplunger 11.

.It will now appear that trigger motor 26 is 25 well able to operate at a frequency substantially in excess of the firing capacity of the gun.- Furthermore solenoid lag is negligible since field winding is adapted to be constantly energized during operation of the trigger motor. 38 As noted above, trigger motor 25 is periodicallyactuated by. timing mechanism 28 (Figure 1) which is operated directly by the airplane -motor.' With reference to Figure 4, timing mechanism 28 includes a casing 83 having a 35 reduced bottom extension 84 on one side of which is formed an annular fiange 85. Flange 85 is adapted to be secured to a ring 86, which,

' a as better shown in Figure 1, extends from the rear of motor 2|. Referring back to Figure 4,

40 a flanged-ring 81 is clamped between flange 85 and motor ring 86, and in turn clamps in place an antifriction bearing 88 Y which rotatably, mounts a shaft 88,'which is connected to the motor shaft (not shown). The outer end 88a 46 of shaft 88 carries a bevel gear I88, which may be keyed -or otherwise connected to the shaft, and is held thereon as by a nut I8I threaded onthe end of the shaft.

, Housing extension 84 is-prbvided with a shoul- 50 dered recess I82 in which an antifriction bear-- ing I83 is disposed to carry. the lower end of a shaft I84. At the junction of casing 83 and:

casing extension 84, a partition I85 is formed, this partition having a bore in which another 55 antifriction bearing I86 is placed and held pref erably by a force fit. Shaft I84 has a reduced portion I84a in bearing I86, and thus the shaft is rotatably mounted. in the casing. The lower end of shaft I84 has pinned thereto a bevel gear I81 which meshes with bevel I88, these gears.

preferably being so cut as to provide a 1 to 2 reduction therebetween. Thus shaft 88 and gear I88- rotate at motor speed, whereas gear I8] and shaft I84 rotate at one-half of motor speed, To

65 prevent escape of lubrication from the bottom of casing extension 84 upwardly into thecasing 'proper, we have provided a suitable gland I88 which is held in place by acap I88v or the like secured to partition I85 by screws H8.

10 The upper end of shaft I84, which extends into casing 83, is furtherreduced and has pinned thereto so as to rotate therewith, a cage generally ndicated at; III. Cage III includes a hub portion II Ia, which is secured to shaft I84 by a pin- I I2, and a disc-like bottom portion I I lb,

which carries preferably three spring biased cam adjusting devices, one of whifli'is generally ina loosely mounted bushing II4, which in turn,"

pivotally supports the reduced end of a shaft 5. The upper reducedJ-endof this shaft is similarly, mounted in a bushing II8 carried in a top or cover plate I I1, which is held against r a ring II8 by suitable screws extending through plate H1 and threaded into cage bottom IIIb. An arm I28 has a hub I2I, which is secured to shaft II5 substantially centrally thereof by a pin I22. The other end I28a of arm I28 encircles a stud 123, which carries a-pair of weights I24 and I25; disposed on opposltesides of arm end 128a (seealso Figure 6).

A. spring I26 :(Figure 4) is coiled about the lower end of shaft 5 between arm hub I2I and bushing II4, the upper end I260. of the spring extending through a hole in arm I28 (see Figure 6) andthe lower spring end I261)v (Figure 4) extending into a hole formed in bushing II4. With the arm and weights in the position shown in Figure 6, bushing 4 (Figure 4) may. be turned to tension spring 1128, as desired and the tension is maintained by'setting the head of a screw I21, which is threaded into cage bottom IIIb, against the top of bushing II4. It may centrifugal force generated thereby throws each of the sets of counterweights I24 and I25 radi- .ally outwardly from shaft I84 and hence draws each of arms l28 therewith toward the dotted line position shown in Figure. 6. As the weights and arms are equidistantly spaced circumferentially about shaft ,I84, 'thefwhole device is in perfect balance. .This radial movement of arms I28 with respect to shaft I84 results in clockwise rotationof each of shafts II5 as .viewed in Figure 6. H a Y Referring backto- Figure 4, each upper end II5a of each shaft II5 carriesa pair of gears I28 and I28 which are pinned to the shaft by a. pin I38. Preferably gear I28 has less teeth than gear I28 and these gears mesh respectively with a pair of gears I3 I and I32 loosely mounted upper end of sleeve I33 is provided with a tongue I35 which interfits with a slot formed in the bottom endof a sleeve I36, whose upper end carries a single lobe cam I31. Thus sleeves I33 and I36- are coupled together. The upper end of sleeve 134 has a tongue I38 which interfits with a slot formed in a sleeve I38 whose upper end carries a cam I48 similar in contour to cam I31. Accordingly, sleeves I34 and I38 are coupled together. The earns, the sleeves and gears I3I and I32 are held against axiaidisplacement from shaft I 84 by a screw I4I threaded into the top of shaft I04. Sleeves I33, I34, I36 and I39 are all rotatable with respect to shaft I04. Also, coupled sleeves I33 and I36 are rotatable relative to coupled sleeves I34 and I39.

As is more. clearly shown in'Figure 11, inner coupled sleeves I34 and I39 are oscillatable as a unit about shaft I04 by reason of meshing gears I29 and I32. Similarly, coupled sleeves I33 and I36 are oscillatable as a unit about shaft I04 and are also movable relative to inner sleeves I34 and I39 by reason of meshing gears I28 and I3I. Relative movement between the pairs of coupled sleeves occurs only upon a variation. in speed of the propeller motor which'drives the timing device.

When shaft I04 is at rest, the circumferential distance between lobes I310. and HM on cams I31 and I40 is small. However, when this shaft and cage III are rotating at a speed sufllcient to generate centrifugal force to effect pivoting of shafts II as pointed out above, gears I3I and I32 are shifted relative to one another and relative to shaft I04, and accordingly shift the positions of cams I31 and I40 so as to separate their lobes to produce a low spot or dwell the extent of which, i. e., the circumferential distance, between lobes I31a and I 40a and also the position of lobes I31a and I40a relative to shaft I04, varies directly as the centrifugal force generated by rotation of cage III and therefore varies directly as the speed of the airplane motor. It will also be obvious from the above that the cams rotate at the same speed as cage III by virtue of their connection therewith through gears I28, I29, I3I and I32.

Still referring to Figure 4, the upper edge of casing 93 has a ring I42 secured therein as by screws I43. A supplemental ring I44 is attached to the top of ring I42 as by screws I45, and holds in place a contact supporting disc I46 havirfg a central opening I41 to provide clearance for the top of shaft I04. Preferably disc I46 is stamped or otherwise fabricated to provide a pair of contact supporting brackets I48 and I49 (Figure 5).

As shown in Figure 4, bracket I49, which is substantially similar to bracket I48, includes a downwardly extending portion I50 and a transverse portio'n I5I. Transverse portion I5I- has a bore coaxial with a bore in disc I46, which receive the ends of a stud I52, disposed between the disc and bracket portion I5I. Stud I52 pivotally supports a cradle I53 which, as is better shown in Figure 5, carries at one end a cam follower I54, and at the other end a contact I55. Contact I55, is insulated from cradle I53 by suitable dielectric washers I56, and a dielectric bushing I51. Contact I 55 is formed on the end of a stud I56 which extends through the end of cradle I53, and this stud also supports one end of a spring conductor I59, whose other end. is

electrically connected to a terminal I 60 which extends through, but is insulated from a plate I6I downstruck from disc I46. Plate I6I also carries another terminal I62 which is electrically insulated from the plate, but is electrically connected to a conductor I63 leading to a contact Contact I64 is carried by-a downstruck portion I65 of disc I46, and this contact cooperates with a contact I66 mounted on one end of, but insulated from a second cradle I61 carried by bracket I48 in substantially the same manner as that pointed out with respect to cradle I53. The other end of cradle I61 has secured thereto a cam follower I68.

Contact I66 is electrically connected to a resilnected with a line I 96 as follows:

lent conductor I69 substantially similar to conductor I59, conductor I69 being electrically connected to a terminal I secured to but insulated from a plate "I downstruck from disc I46. Plate "I also carries another terminal I12 which is electrically connected by a conductor I13 to a contact I14 which cooperates with movable contact I55 on the end of cradle I53. Terminals I10 and I12 are inflow terminals, whereas terminals I60 and I62 are outflow terminals.

It will now appear that as shaft I04 carrying cams I31 and I40 rotates, followers I68 and I54,-

respectively, are moved to effect engagement between contacts I66, I64 and I55, I14, respectively. When the followers hit the dwell or low spot between lobes I31a and (0a (Figure 8) contacts I55 and I66 (Figure 5) cooperate with their respective cooperating contacts I14 and I64 because of the bias of resilient conductors I59 and I69.

The upper part of timer casing 93 has'suitably secured thereto a housing I in which a bracket I150. is attached. This bracket carries a solenoid I16 having a core I 11 arranged to attract a pivoted armature I18 when the solenoid is energizecl. As will be described in greater detail hereinafter, solenoid I16 is energized from a battery when a. switch is closed by the pilot of the airplane, and resulting attraction of armature I18 against the bias of a spring I19 to depress a hook-300. This closes contacts I82, I82a and I83, I 93a (Figure 8) to permit a flow of current to terminals I10 and I12 (Figure 5) which are c'onencted as described to the timer contacts or breaker points I55 and I66. Current is supplied to solenoid I16 from a socket I80 having terminals I80a. and I80b adapted to receive a plug (not shown) leading from the battery and the" pilots control switch 34. An electrical connec tion I8I having terminals I8Ia, I8") and I8Ic is carried by housing I15, this connection being adapted to receive a cable carrying wires 26 and 21 and 0 (Figures 1 and 8) which connect the timer 28 to the trigger motor 25.

*With reference now to Figure 8, which diagrammatically shows the electric circuit by which trigger motor 28, timer 25, battery 36 and pilot switch 34 are connected. Battery 36 is connected to line 33 which, with line 32, is preferably disposed in a cable (not shown) terminating in a plug having a pair of terminals I85 and I86 for lines 32 and 33. Lines 32 and 33 are connected upon closing of pilot switch 34. When the plug which carries terminals I85 and I86 is plugged into socket I80 of the timer 28, terminal I85 mates with terminal I80a. to connect line 32 to a line I 81 whose other end is connected to solenoid winding I16. As noted above the other end of solenoid winding I16 connects with a wire I84 leading to'ground G, and hence back to battery 36. Completion of this circuit by the closing of pilot switch 34 energizes solenoid I16 and attracts armature I18 to close contacts I82, I82a and contacts I83, I83a. Contacts I82a and I83a are connected to a line I88 leading to terminal I801; which mates with terminal I86 of line 33.

When contacts I83 and I83a are closed byenergization of solenoid I16, battery 36 is con- Battery 36, line 33, terminals I86 and I80b, line I88, contacts I83a, I83. Line I96 runs to terminal I8Ic of connection I8I and mates with a terminal I 91 on the end of line 26 when this line isplugged in. The other end ofline 26 has a. terminal I98 which with-a line I98 also connected to binding post' I60.- This bindlngpost is connected by a wire I94 '.'--to terminal I8Ib of electrical connection I8I and is adapted tomate' with a terminal I95 connected Armature aaaasoa mateswith field coil terminal 84 in trigger motor 28, the other end of field coil 5| being connected toa line I99 which is connected to ground G as follows: Terminals 86 and t 200, ground line .0,

terminals I, I8Ic, line I84, hence to ground.

I89. whichleads to timer terminal-or binding post; I10.- This last terminal has connected thereto .wires I90 and I9I, which are respectively connected to stationary timer contact I14 andmovw ,able timer contact I66. Hence,iwhen-timer con- 1 tacts- I55'and I14are closed, wire I90 is conisnectedtto a line I92, which isconnected to timer terminal-orbinding post I80. wwhentimer con-' tacts I64 and I66 are-closed,-*line I9l is in circuit to line 21-when the cable (notshownlwhich carries lines 26, 21 and g is plugged into connece tion I8I.-. 1 The other end of line 21 has afterminal 202 adapted to mate with terminal 85, which'is 'connected to armature coil 58 of timer 25. The other, end-of the armature coilis connected-to line I99 and hence to ground Gas noted above fwith respect to field coil 5|.

-It will now appear that when the pilot closes" pilot switch 34, solenoid I18 is energized to close armature contacts I82, I'82a and I83, I83a. .Clo'sing of these contactscompletes' the circuits to field coil 5I and armature coil 58 of trigger "motor 25; It should be herenoted'that whena pilot switch'94 is'closed, fleldcoil 5| is constantly 1 energized whereas armature coil 58 is intermittently energized by virtue of cams I91 and I40 of v the timing mechanism.

The simplicity and reliability of our synchroniz ingsystem substantially precludes thenecessity of subsequent adjustment or carefafter initial installation and setting, As there are no moving,

partsutilized totransfer impulses from the timer to the tri ger motor; temperature variations have v no effect on the operation of the system.

j As noted abover cams I81 and I40 are.rela-H tively movableand their lobes I81a"and I 40a are near together or.-far apart, depending upon "the enginespeed. Asthecamlobes separatathe low spot or dwell therebetween increasesrthis dwell increasing in extent as the motor speed rises, and

it is only when eitherof the followers? I54 or I68 is engaging the dwell that current ilowsto the" trigger motor annature 58; As hereinbefore noted, there are certain constant time elemen s which cause a time lagbetween closing 'of contacts I55. I14 or 168, I64, and nassingof the J bullet through the plane of. rotation of the pro peller, and this time lagis compensated .i'or M the. variation in the phase relationship or, in a other words, by the shift of cams 431 and Ian I counterclockwise relative. to shaft I04 as the;

engine speed increases Thus when the motoris speededup, the dwell increasesin extent andthe position ,of closing. of contact is also advanced I relative to the. motor shaft and hence propeller blades so that the electricimpulse is transmitted sooner, and hencethe gun is fired sooner, with-a the ultimate result that the bullet passes .through 1 the median ,line between propeller blades regardless of the rate at which the propeller is whirling.= In efl'ect, the gun is shot sooner or later after the passage of an oncoming propeller; blade through the line of fire of the gun-ac-.

terminal I82 is connected to a'line' 5v cordingly as the propeller is rotating faster or slower.

R. P. M. (approximately toppropeller speed).';-

Conversion of time into arc of propeller rotation in 1/1000 second" R. P. M. Degrees Time lag factors (approwimatw 1 v a v v Seconds Firing pin fall after release of sear .005 t Primer lag and bullet travel to gun muzzle- .00l5 v,

Bullet travel' muzzle. to the plane of rotation or the propeller (4' .0015 Synchronizer delay (timer contact to sear release) i 1.1.00 7

Total time 1 g L;;, .0150.

Rotation of propeller during time. period At 3000 a; P. lag=l8 X 15:270 At 800 R. P. M.,'lag=4.8 15=72 J i Amount of automatic correction, 198i Hence the zero .shot for a dead engine should occur .at substantially 72 ahead of a line bisecting the angle between two propeller blades; or-l2 ahead-of the center line of any blade of a three- I bladed propeller. This timing would maintain the theoretical point of bullet passage through the plane of rotation. of the propeller at a point midway between the blades for all engine; speeds 1 between 800 and 3000. R. P. M., It will beunderstood, that these figures are. approximations and are notrto be construed ;in a limitating sense, but as illustrative of the automaticcorrection aflorded byour synchronizing system.

Undercertain circumstances it may be desirable, or in some instances even necessary,to ,reduce the trigger motor lag still further. This is accomplished by .reducing the reaotance of the armature coil circuit in the impulse motor to a minimum in order first, to allow rapid buildup of the armature currentto a maximum and accordingly to reduce the over all time lag of operationtoa minimum, and, second, to reduce the arcing of the timer contacts and hence to increase their life. To this end, the fragmen tarymodification. oi the impulse motor shown in Figure '7 is directed. This form of motor is similar in many respects to the motor shown in .7 Figure 2, and accordingly includes field winding. 5|, core 49, cap or cover 53, bracket 6i and cage,

51 with its associated moving parts as described above. 'Cage 51 thus includes armature coil58 which floats in air gap 55. Associated vwith ary mature coil 56andelectrically'connected there with are a set of compensation coils 203 and 204 preferably arranged respectively above and below coil 58 as shown in Figure 7. Coils203 and 204, as 7 shown in Figure}, are connected in series with.

the main armature coil 58; and together have,

the same. numberoi turns as the main armature coil. Howeventhe. compensating coils are'oppo-,-

sitely wound with respect to armature-coil 58 so that their flux linkage or polarity will be in the opposite direction to the main armature coil flux linkage. In all other respects the circuit in Figure 9 is the same .as that in Figure 8, and the operation of this modification is substantially the same as that of the trigger motor in Figure 2,

with the exceptions noted.

With reference to Figure 10, wherein there is shown a fragmentary section of a third form of trigger motor, a cage generally indicated at 208 floats in air gap 55 as described with respect to motor 25 in Figure 2; -Cage 205 includes an annular super-structure 200, in the interior of which is formed guiding and suporting surfaces generin operative position the outer peripheral edge 2l5 of lower resilient diaphragm 2.

The inner edge 2 of diaphragm 2" supports cage 20! and is insulated therefrom by insulator Illa, and is also electrically connected to coil 55. A contact M6 is electrically connected to diaphragm 2|! by way of a rivet or screw 2H which is" insulated from bracket 2 I 2. It may now be seen that lower diaphragm 2l3, through its conductivity. affords a good electrical connection between coil 55 and contact 2I8, whereas the resiliency of both diaphragm 209 and 2|! bias cage 205 toward its bottom position as shown in Figure 10, upon deenergization of armature coil 58, as hereinbefore described.

From this description it is. readily apparent that each of the diaphragms 209 and Ill provide a means whereby the cage and plunger are permitted limited travel in a direction parallel to the longitudinal axis of the plunger with substantially no movement in a direction transverse to said axis.

Accordingly we have provided a synchronizing system for a machine gun which efllclently and practically attains the various objects hereinbe: fore set forth.

As many possible embodiments may be made of the above inventionand as many changes might be made in the embodiment above set forth, it is to be understood that all matter hereinbefore set forth, or shown in the accompanying drawings, is to be interpreted as illustrative and not in a limiting sense.

We claim:

1. A synchronizing system of the character described for synchronizing the fire of a machine gun with respect to a motor driven airplane propeller so as to fire through the plane of rotation of the propeller between adjacent blades comprising, in combination, an electrically actuated firing mechanism including an impulse device as sociated with the firing mechanism of said gun, said impulse device including means for creating a substantially permanent magnetic flux and an intermittently excitable member which when energized is adapted to create an impulse which operates said gun firing mechanism, a circuit including a source of power connected to said device, and means for intermittently energizing said circuit to excite said device and thereby create a firing impulse.

2. A synchronizing system of the character described for synchronizing the fire of a machine gun with respect to a motor driven airplane propeller so as to fire through the plane of rotation 01 the propeller between adjacent blades comprising, in combination, an electrically actuated firing mechanism including an impulse device associated with the firing mechanism of said gun, said impulse device including means for creating a substantially permanent magnetic fiux and an interm ttently-excitable member which when energized is adapted to create an impulse which operates said gun firing mechanism, a circuit including a source of power connected to said device, means for intermittently energizing said circuit to excite said device and thereby create a firing impulse, and means operated by the propeller motor for energizing said circuit at predetermined times so that the firing impulse is so timed that the gun fires between adjacent blades of the propeller.

3. A synchronizing system of the character described for synchronizing the fire of a machine gun with respect to a motor driven airplane propeller so as to fire through the plane of rotation of the propeller between adjacent blades comprising, in combination, an electrically actuated firing mechanism including an impulse device associated with said gun, said impulse device including means for creating a substantially permanent magnetic fiux and also an excitable member which when energized creates a magnetic fiux whose lines of force are opposed to those of said means, movable means associated with said member adapted to operate the firing mechanism of the gun upon creation of an impulse, and means for exciting said member intermittently in timed relation to propeller rotation so that the gun fires only between adjacent propeller blades.

4. A synchronizing system of the character described for synchronizing the fire of a machine gun with respect to a motor driven airplane propeller so as to fire through the plane of rotation of the propeller between adjacent blades comprising, in combination, an electrically actuated firing mechanism including an impulse device associated with said gun, said device having two elements which when energized create an impulse which operates the firing mechanism of the gun, means for maintaining one of said elements constantly energized whereby said impulse is created immediately upon energization of the other of said elements without the lag which would otherwise occur, and means for intermittently energizing the other of said elements to create said impulse.

5. A synchronizing system of the character described for synchronizing the fire of a machine gun with respect to a motor driven airplane propeller so as to fire through the plane of rotation of the propeller between adjacent blades comprising, in combination, an electrically actuated firing mechanism including an impulse device associated with said gun, said device having two elements which when energized create an impulse which operates the firing mechanism of the gun, means for maintaining one of said elements constantly energized whereby said impulse is created immediately upon energization of the other of said elements without the lag which would otherwise occur, means for intermittently energizing the other of said elements to create said impulse, and means for reducing the reactance in said second-mentioned element tion thereof.

6. A synchronizing system of the character described for synchronizing the fire of a machine gun with respect to a motor driven airplane pro- .upon energizapeller so as to fire through the plane of rotation of the propeller between adjacent blades comprising, in combination, an electrically actuated firing mechanism including an impulse device associated with said gun, said device having two elementswhich when energized create an impulse which operates the firing mechanism of the gun, means for'maintaining one of said elements constantly energized whereby said impulse is created immediately upon energization of the other of said elements without the lag which would otherwise occur, means for intermittently energizing the other of said' elements to create said impulse, said second-mentioned element including a coil, and coilmeans whose polarity is opposite to that of said second-mentioned element whereby upon energization of said coil and said coil means reactance in said element is substantially neutralized.

7. An impulse motor adapted to be connected to a machine gun for actuating the sear pin thereof, said motor comprising, in combination, a casing, a field coil disposed about a metallic core and mounted in said casing, said field coil being adapted to be constantly energized to create a substantially permanent magnetic flux, a movable armature coil adapted to be intermittently "energized and disposed within the magnetic field created by said first-mentioned coil, a sear operating plunger connected to said armature coil and movable therewith upon energization thereof from a normal to an extended position, and means-for reducing the reactance of said arma ture coil upon energization thereof.

8. An impulse motor adapted to be .connected to a machine gun for actuating the sear pin thereof, said motor comprising, in combination, a casing, a field coil disposed about a metallic core and mounted in said casing, a movable coil 40 support mounted in said casing for movement away from and toward said core, an armature coil mounted on said support, said field coil being adapted to be constantly energized so that upon energization of saidarmature coil said support is impelled away from said core, and a member secured to said support and adapted upon movement thereof to strike said sear to fire the gun, the end of said-member being spaced from the end of said sear so that said member strikes said sear with a hammer blow.

, 9. A synchronizing system of the character described for synchronizing the fire of a machine gun with respect to a motor driven airplane propeller so as to fire through the plane of rotation or the propeller between adjacent blades comprising, in combination, a firing-mechanism including an electrically actuated impulse device operatively associated with said gun and adapted upon energization- .to fire the gun, said impulse device including, means for creating a substantially permanent magnetic flux and an intermit tently excitable-member which when energized is adapted to create an impulse, means for utilizing said impulse to fire the gun, a circuit including a source of power connected to said device. and means for intermittently energizing said circuit to excite said device and thereby create a firing impulse.

10. An impulse motor adapted to be connected h: to a machine gun for actuating the .sear' pin to a machine gun for actuating the sear pin thereof, said motor comprising, in combination, a casing, means in said casing for creating a sub-' stantially permanent magnetic flux, said means including a core and field coil disposed thereabout, means forming an air gap at one end of a said core, a cylindrical member reciprocably disposed in said gap, an energizable armature coil mounted on said cylindrical member, said coil when energized being adapted to create an impulse which elfects movement of said member, means for biasing said member oppositely to the effect of said impulse, and a part secured to said support and adapted to coact with said sear pin upon creation of an impulse.

11. An impulse motor adapted to be connected to a machine gun for actuating the sear pin thereof, said motor comprising, in combination, a casing, means in said casing for creating a sub-- stantially permanent magnetic flux, said means including a core and field coil disposed thereabout, means forming an air gap at one end of said core, a cylindrical member reciprocably disposed in said gap, an 'energizable armature coil mount-. ed on said cylindrical member, said coil when energized being adapted to create an impulse which efiects movement of said member, means for biasing said member oppositely to the eiiect of said impulse, a plunger associated with said member and adapted to coact with said sear pin upon the creation of an impulse, and means mounting said plunger on said member for limited movement with respect thereto in directions. other than axial.

I 12; An impulse motor adapted to be connected thereof, said motor comprising, in combination, a casing, means in said casing for creating a substantially permanent magnetic .fiux, said means including a core and field coil disposed'thereabout, means forming an air gap at one end of said core, a cylindrical member reciprocably disposed in said gap, an .energizable armature coil mounted on said cylindrical member, said coil when energized being adapted to create an impulse which effects movement of said member, means for biasing said member oppositely to the eifect of said impulse, a plunger associated with said memberand adapted to coact with said sear pinuponthe creation of an impulse, means mounting said plunger on said member for limited movement with respect thereto in directions other than axial, and means constantly urging said, plunger into a coaxial position with respect to said member. i

13. An impulse motor adapted to be connected to a machine gun for actuating the sear pin thereof, said motor comprising, in combination, a casing, means in said casing for creating a substantially permanent magnetic flux/ said means including a field coil disposed about a metallic core, a cylindrical member movably disposed wlthin said casing adjacent'one end of said core and substantially coaxial therewith, an armature coil carried by said member adapted upon energization-to create an impulse which 66 IRVING W. DOYLE. 10 

